KR20090107257A - A magneto rheological fluid - Google Patents

Abstract

PURPOSE: A magneto rheological fluid is provided to reduce viscosity variation according to the temperature change and increase yield stress when applying a magnetic field. CONSTITUTION: A magneto rheological fluid includes a magnetic particle, a dispersion medium, and a dispersant. The dispersion medium includes a mixture. The mixtures contains the hydrocarbon oil and ester of 2:8 to 8:2. The dispersion medium has the weight of 5 to 60 and the dispersant has the weight of 0.1 to 10. An average diameter of the magnetic particle is 1 to 100 um. The magnetic particle includes one or two groups among the iron, nickel, cobalt, carbonyl iron, soft ferrite and the alloy thereof.

Description

A magneto rheological fluid

The present invention relates to a magnetorheological fluid, and more particularly to a magnetorheological fluid comprising a mixture of synthetic hydrocarbon oil and ester as a dispersion medium.

Magnetorheological fluid is a material that reversibly changes the viscosity characteristic of a fluid according to the strength of an externally added magnetic field, and is one of intelligent materials. Specifically, the magnetorheological fluid is obtained by dispersing iron, nickel, cobalt, and magnetic alloys of fine particles of several to several tens of microns in diameter in a dispersion medium such as mineral oil, synthetic hydrocarbon, water, silicone oil, and esterified fatty acid. Refers to a non-colloidal suspension.

The magnetorheological fluid has a large variation in the flow characteristics such as the viscosity characteristic of the fluid as the magnetic field is applied, and has excellent durability. In addition, they are relatively less sensitive to contaminants and have a very fast and reversible response to magnetic fields of 10 ^-3 seconds. For this reason, it is evaluated that it is highly applicable to various industrial fields such as vibration control devices such as clutches of automobiles, engine mounts, dampers, high-rise seismic devices, and driving devices of robotic systems. It also has significant advantages over other controllable fluids, such as electrorheological fluids.

Magnetorheological fluids exhibit the properties of Newtonian fluids when no magnetic field is applied. However, when a magnetic field is applied, the dispersed particles form a dipole to form a fibrous structure in a direction parallel to the applied magnetic field, and the fibrous structure increases the viscosity and thus has a shear force or a resistance to flow that interferes with the flow of the fluid. Yield stress is greatly increased. Yield stress at this time increases with the strength of the magnetic field.

In order to effectively use such a magnetorheological fluid, the magnetorheological fluid should have a high yield stress and the magnetic particles should be uniformly distributed in the dispersion medium. In addition, the viscosity of the fluid must be low enough so that the fluid can quickly return to its original state unless the magnetic field is applied again after applying the magnetic field. In addition, there is little change in viscosity due to the change of temperature, so it should always show a constant flow characteristic.

However, magnetorheological fluids are severely hampered by rheological behavior due to gravitational precipitation problems. The main reason for this precipitation is that the density of the dispersion medium is approximately 0.5 to 3 g / cm 3, whereas the density of the magnetic particles is about 7.86 g / cm 3 and the density of the magnetic particles is much larger than that of the dispersion medium. This is because they tend to precipitate in the dispersion medium. Due to the precipitation of the magnetic particles as described above it is technically very difficult to secure a good dispersion stability of the magnetorheological fluid.

Many methods have been tried to date to prevent the sedimentation of magnetic particles in the magnetorheological fluid to improve dispersion stability of the magnetorheological fluid.

U.S. Patent 6638443 discloses magnetorheological fluids using polyalphaolefins (PAO) and diesters as a dispersion medium. However, the PAO has a disadvantage of expensive price and the dispersion medium prepared therefrom has a disadvantage of poor solubility of the additive.

Therefore, the necessity of developing a magnetorheological fluid with improved dispersion stability has been constantly emerging.

An object of the present invention is to provide a magnetorheological fluid having improved dispersion stability and heat resistance, high yield stress upon application of a magnetic field, low viscosity change due to temperature change, and good sedimentation stability and redispersibility. In addition, the present invention provides a magnetorheological fluid having low manufacturing cost and excellent viscosity index and additive solubility.

In order to solve the above problems, the present invention is a magnetic particle; A dispersion medium comprising a hydrogenated hydrocarbon oil prepared by hydrogenation from mineral oil, and a mixture comprising an ester in a weight ratio of 2: 8 to 8: 2; And it provides a magnetorheological fluid comprising a dispersant.

The magnetorheological fluid of the present invention has improved dispersion stability and heat resistance, high yield stress upon application of a magnetic field, low viscosity change due to temperature change, and excellent sedimentation stability and redispersibility. In addition, the manufacturing cost is low, and the viscosity index and additive solubility are excellent.

Hereinafter, the present invention will be described in detail.

The magnetorheological fluid of the present invention includes magnetic particles, a dispersion medium and a dispersant.

The magnetic particles of the present invention form a dipole when the magnetic field is applied to the magnetorheological fluid, and are arranged in a row. As a result, the magnetorheological fluid increases in viscosity to change into a solid form. In addition, when the magnetic field is removed, the dipole loses force and the magnetic particles are scattered irregularly, causing the magnetorheological fluid to return to its original state.

The magnetic particles preferably have an average diameter of 1 to 100 µm, more preferably 1 to 20 µm. In general, the yield stress of the magnetorheological fluid increases in proportion to the particle diameter and the dispersion stability is inversely proportional to the particle size. Accordingly, when the average diameter of the magnetic particles satisfies the above-described range, there is an advantage that the yield stress is increased and the dispersion stability is excellent.

The magnetic particles preferably include one or two or more selected from the group consisting of iron, nickel, cobalt, carbonyl iron, soft ferrite and alloys thereof. In addition, the magnetic particles may be purchased commercially, for example, carbonyl iron particles of BASF (Carbonyl Iron Powder CD, CM, HS) may be used.

The dispersion medium of the present invention serves as a lubrication medium in magnetorheological fluids and to dissolve functional additives including a dispersant.

The dispersion medium of the present invention comprises a mixture of hydrogenated hydrocarbon oils prepared by hydrogenation from mineral oil, and esters. Hydrogenated hydrocarbon oil and ester in the mixture is preferably included in the weight ratio of 2: 8 to 8: 2, more preferably in the weight ratio of 4: 6 to 6: 4. When the above-mentioned range is satisfied, the magnetorheological fluid including the dispersion medium has a low sedimentation degree, excellent magnetorheological properties, that is, a good upuring ratio (TUR), high redispersibility, and low viscosity change due to temperature change. have.

More preferably, the hydrogenated hydrocarbon oil has a pour point of -50 to -10 ° C and a flash point of 140 to 270 ° C. If the above-described temperature range is satisfied, the magnetorheological fluid may operate as a fluid at a relatively inexpensive and general operating temperature range of automobiles and electronic products.

The hydrogenated hydrocarbon oil is NEXBASE 3020 (brand name, manufacturer: NESTE OIL), NEXBASE 3030 (brand name, manufacturer: NESTE OIL), YU-L3 (brand name, manufacturer: SK Energy), YU-3 (brand name, manufacturer: SK Energy) , YU-4 (trade name, SK Energy), YU-6 (trade name, SK Energy), YU-8 (trade name, Manufacturer: SK Energy), Ultra-S2 (trade name, S Oil), and Ultra -s3 (trade name, manufacturer: S Oil) is preferably one or two or more selected from the group consisting of. More preferably, it is 1 type, or 2 or more types chosen from the group which consists of NEXBASE 3020, NEXBASE 3030, YU-L3, and YU-3.

The ester has a pour point of -80 to -50 ° C, and a flash point of 160 to 230 ° C. If the above temperature range is satisfied, the magnetorheological fluid may operate as a fluid in the general operating temperature range of automobiles and electronic products.

The ester is one or two selected from the group consisting of DOA (Di Octyl Adipate, manufacturer: LG Chem), DIDA (Di Iso Desyl Adipate, manufacturer: LG Chem), and DINA (Di Iso Nonyl Adipate, manufacturer: LG Chem). It is preferable that it is a species or more.

The dispersion medium is preferably contained in an amount of 5 to 60 parts by weight, and more preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic particles. When included in the above range, it can act as a lubricating medium in the magnetorheological fluid without significant increase in manufacturing cost, there is an effect that the dissolving power of the functional additives including the dispersant is excellent.

The dispersant of the present invention serves to prevent reaggregation of the magnetic particles. The dispersant preferably comprises at least one polar group selected from the group consisting of amino group (-NH ₂ ), hydroxy group (-OH) and carboxyl group (-COOH). The dispersant is preferably one or two or more selected from the group consisting of oleic acid, fatty acid metal soap, polyalcohol, ammonium salt, fatty acid, polyethylene oxide, phosphate and phosphonate.

The dispersant is preferably included in an amount of 0.1 to 10 parts by weight, and more preferably 1 to 5 parts by weight, based on 100 parts by weight of the magnetic particles. When included in the above-described range, there is an advantage of preventing reaggregation of magnetic particles without a significant increase in manufacturing cost.

The magnetorheological fluid of the present invention improves dispersion stability and heat resistance, has a high yield yield stress, which is a magnetic field, has a low viscosity change due to temperature change, and has excellent sedimentation stability and redispersibility. In addition, the manufacturing cost is low, and the viscosity index and additive solubility are excellent.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are for the purpose of explanation and are not intended to limit the present invention.

Example  1 to Example  5, and Comparative example  1 to Comparative example  3: Magnetorheological  Produce

The magnetic particles, the dispersion medium and the dispersant were added in the ratio of the following Table 1 and stirred for 30 minutes at 1,000rp using a Homer mixer and then put into a ball mill to mill for 24 hours to prepare a magnetorheological fluid.

division Magnetic particles Distributed media Dispersant Example 1 A-1 500 g B-1: B-2 50 g: 50 g = 100 g c-1 6 g Example 2 A-1 500 g B-1: B-2 20 g: 80 g = 100 g c-1 6 g Example 3 A-1 500 g B-1: B-2 40 g: 60 g = 100 g c-1 6 g Example 4 A-1 500 g B-1: B-2 80 g: 20 g = 100 g c-1 6 g Example 5 A-1 500 g B-1: B-2 60 g: 40 g = 100 g c-1 6 g Comparative Example 1 A-1 500 g B-1 100 g c-1 6 g Comparative Example 2 A-1 500 g B-1: B-2 10 g: 90 g = 100 g c-1 6 g Comparative Example 3 A-1 500 g B-1: B-2 90g: 10g = 100g c-1 6 g

A-1: Carbonyl Iron Powder CM (trade name, manufacturer: BASF Corporation)

B-1: NEXBASE 3020 (brand name, manufacturer: NESTE OIL)

B-2: DOA (manufacturer: LG Chem)

C-1: oleic acid

Test Example : Characterization

The properties of the magnetorheological fluids of Examples 1 to 5 and Comparative Examples 1 to 3 were measured by the following method and are shown in Table 2.

① Sedimentation intensity (%):

Measured based on ASTM D869-85, the volume of the supernatant two weeks after preparation divided by the total volume of the magnetorheological fluid was expressed as a percentage.

②TUR (Turn Up Ratio) measurement

The instrument used for the measurement is the MCR301 rheometer of Parr, Germany, which has a plate-plate geometry (diameter 20 mm), a gap size of 0.9 mm, a magnetic field which can vary from 0.1 to 1.0 tesla, and a shear rate of 0 to 1,000 ( Up to 1 / sec).

The viscosity value of the magnetorheological fluid when 0.2 Tesla is applied to the device is divided by the viscosity value of the magnetorheological fluids of Examples 1 to 5 and Comparative Examples 1 to 4 in the off state. It was. TUR value was carried out at 25 ℃, shear rate 1,000 (1 / sec).

③ Redispersibility Measurement

100 ml of the magnetorheological fluids prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were placed in 100 ml of transparent plastic bottles, and left for 2 weeks. Shake the plastic bottle up and down vigorously for about 1 minute after 2 weeks, then pour the bottled fluid into a new beaker, and after 5 minutes, if the volume of fluid remaining in the plastic bottle is less than 1% High, less than 1 to 5% If the back side is Medium, and if it is 5% or more, it was determined as Low.

④ Measurement of viscosity change (△ η / △ T) according to temperature change of magnetic rheological fluid

The measured temperature measured the viscosity change value of 25 degreeC and 80 degreeC.

Sedimentation degree (%) TUR Redispersibility Δη / △ T Example 1 2.5 1.90 height 8.1 Example 2 2.1 1.83 height 7.7 Example 3 2.4 1.85 height 7.9 Example 4 8.2 1.92 middle 8.9 Example 5 2.6 1.91 height 8.2 Comparative Example 1 14.0 1.94 lowness 10.3 Comparative Example 2 1.8 1.82 height 7.6 Comparative Example 3 13.2 1.93 lowness 9.4

Referring to Table 2, the sedimentation degree is less as the content of the ester increases, it can be seen that the TUR value is excellent as the content of the hydrogenated hydrocarbon oil. It can be seen that the magnetorheological fluid of the present invention is relatively excellent in TUR, low sedimentation degree, and excellent redispersibility. In addition, the viscosity change with the temperature change is small. On the other hand, in the case of Comparative Example 2, the sedimentation degree is low, but the TUR is not good, and there is a problem in durability such that hydrolysis reaction occurs when used for a long time.

Claims (9)

Magnetic particles; A dispersion medium comprising a hydrogenated hydrocarbon oil prepared by hydrogenation from mineral oil, and a mixture comprising an ester in a weight ratio of 2: 8 to 8: 2; And Magnetorheological fluid, characterized in that it comprises a dispersant. The method according to claim 1, Based on 100 parts by weight of the magnetic particles, The dispersion medium is 5 to 60 parts by weight; And Magnetorheological fluid, characterized in that the dispersing agent is included in 0.1 to 10 parts by weight. The method according to claim 1, Magnetorheological fluid, characterized in that the average diameter of the magnetic particles is 1 to 100㎛. The method according to claim 1, The magnetic particles are magnetorheological fluid, characterized in that it comprises one or two or more selected from the group consisting of iron, nickel, cobalt, carbonyl iron, soft ferrite and alloys thereof. The method according to claim 1, The hydrogenated hydrocarbon oil is a magnetorheological fluid, characterized in that the pour point is -50 to -10 ℃, flash point is 140 to 270 ℃. The method according to claim 1, The ester has a pour point of -80 to -50 ℃, flash point is a magnetorheological fluid, characterized in that 160 to 230 ℃. The method according to claim 6, The ester is a magnetorheological fluid, characterized in that one or two or more selected from the group consisting of DOA (Di Octyl Adipate), DIDA (Di Iso Desyl Adipate) and DINA (Di Iso Nonyl Adipate). The method according to claim 1, The dispersant is a magnetorheological fluid, characterized in that it comprises one or two or more polar groups selected from the group consisting of amino groups, hydroxyl groups and carboxyl groups. The method according to claim 8, The dispersant is one or two or more selected from the group consisting of oleic acid, fatty acid metal soap, polyalcohol, ammonium salt, fatty acid, polyethylene oxide, phosphate and phosphonate.